Pixel Circuit Threshold Compensation via Shared Gate Transistors
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Solution Overview
Problem
The luminance of LEDs in existing pixel circuits is unstable due to threshold voltage shifts in driving transistors, which affect the consistency of the driving current and thus the brightness of the LEDs.
Innovation Solution
A pixel circuit design that includes a compensation circuit, a driving circuit, a light-emitting diode, a capacitor, and an external power supply, where the compensation circuit sets a voltage for the node based on a scanning signal, and the driving circuit generates a driving current using this voltage and the threshold voltage of the driving transistor, with both transistors sharing a gate electrode to stabilize the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a basic pixel circuit with one capacitor and two transistors is used, then the circuit structure is simple, but the luminance of LEDs is unstable due to threshold voltage shifts in the driving transistor
Solution Approach 1:
The pixel circuit is divided into distinct functional modules: a compensation circuit (with transistors T21, T22, T23 and capacitor C21) and a driving circuit (with transistors T24, T25 and capacitor C22). This segmentation allows the compensation circuit to specifically address threshold voltage shifts while the driving circuit maintains LED operation, resolving the contradiction between simple structure and stable luminance.
Solution Approach 2:
The compensation circuit performs preliminary compensation for threshold voltage shifts before the driving circuit operates. During the data writing stage, the compensation circuit pre-charges capacitor C21 with the threshold voltage value, which is then used to compensate for threshold shifts during subsequent light-emitting stages, ensuring stable luminance from the outset.
2Device complexity
If the power supply ELVDD and data signal are spaced only by transistor T25, then the circuit structure is compact, but the data signal is influenced by the power supply due to leakage current in T25, affecting luminous stability
Solution Approach 1:
Transistor T24 is introduced as an intermediary component between the power supply ELVDD and the data signal path. During the data writing stage, T24 is turned on to provide an additional current path that isolates the data signal from the power supply, preventing leakage current from affecting the data signal and ensuring luminous stability while maintaining a compact structure.
3Reliability
If threshold compensation circuits are added to eliminate threshold shift influence, then luminance stability is improved, but the circuit complexity increases
Solution Approach 1:
The compensation circuit and driving circuit are merged into a single integrated pixel circuit structure that shares common components and control signals. The compensation transistors T21-T23 and driving transistors T24-T25 are controlled by coordinated control signals (Sn, Sn-1, En) to achieve both compensation and driving functions within a unified circuit architecture, minimizing overall complexity while ensuring luminance stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design stabilizes the luminance of the LEDs by isolating the data signal from the external power supply during the data writing stage and ensuring that the driving current is not influenced by threshold voltage drift, resulting in improved luminous stability.
Implementation Method 1
a capacitor C21 begins to store electric charges so that a gate voltage of T21 is gradually decreased to a value of (Vdata+VTH)
Implementation Method 2
A driving current generated by T11 allows a LED EL11 located between a first power supply ELVDD and a second power supply ELVSS to emit light
Data Source
AI summary
A pixel circuit, a driving method and a display, comprising: a compensation circuit (1) being electrically connected to a driving circuit (2) via a first node (N1); an external power supply (ELVDD), the driving circuit (2) and a light-emitting diode (EL4) being connected in series; a capacitor (C3) being located between the first node (N1) and the external power supply (ELVDD), wherein the compensation circuit (1) is used for setting the voltage of the first node (N1) to a first voltage (Vdata+VthT1) by means of a compensation transistor; the capacitor (C3) is used for maintaining the voltage of the first node (N1) as the first voltage (Vdata+VthT1); the driving circuit (2) externally connects a first control signal (En) to generate a driving current (IEL4) to drive the light-emitting diode (EL4) to emit light; and a driving transistor in the driving circuit (2) and the compensation transistor are common-gate transistors.